Windows 10 w/ Comcast Giganet Service getting only 250 Mbps

For the better part of 6 months, I have been working with Comcast technical support to get close to the speeds that I pay for. I "upgraded" to the Giganet service around that time and have never seen speeds higher than 330 Mbps (typically 80 - 150 Mbps). As I work from home, it's critical for me to be able to access more bandwidth.

I have tried multiple machines (all with Giganet capabilities, all Windows 10) and they never exceed 330 Mbps (wired or wireless). I have tried those same machines in our office and have no problem getting (wired / wireless) well over 600 Mbps.

I now have all new Cat 6 cables, all drivers are up to date, and have tested each machine as the single output from my Arris SB8200 Router. I initially had the Comcast Giganet router and was paying $11/month for it without any higher speeds; Comcast had suggested the Arris SB8200 (supported for Giganet).

Each time Comcast has come out, they use their "line tester" that has no load on it and see speeds at 975 Mbps. They "don't have any laptops that they can use to test the gigabit speeds", but did bring out one that got 650 Mbps (no firewall, no antivirus, Windows 7).

I've tested in in safemode with networking and still see those speeds. I've tried multiple speed tests but Comcast's Xfinity Speed Test has been the fastest of them all (this is the one that Comcast wants me to use). Comcast is pointing the finger at my equipment, but again, these same machines get the speeds in other locals, so I don't believe it is them. Additionally, the router of theirs gives the same performance as my new Arris SB8200.

Any ideas?

Thank you

bro67 Using Speed test - how fast is your internet? | DSLReports, ISP Information i get 282.7 Mbps / 41.9 Mbps.
xTL fast showed 210 Mbps. speedtest showed 286 / 41. I have solid state drives in all of my machines. The one I'm using at the moment is a Dell Precision 7520 laptop, 64-bit, Intel Xeon CPU E3-1505M v6 @ 3.00GHz, 64 GB RAM

I have tried with the firewall and Norton Security disabled and get similar results. I've also updated all of the drivers to the latest available for my hardware.

Try downloading something like a Windows ISO at several different times during the day/night using TechBench by WZT (v4.1.1) or Microsoft Windows and Office ISO Download Tool This is directly from M$ Servers so it'll give a more accurate result of your true speed versus any "Speedtest"

I appreciate the thought, but I think I've already proven out that the speed just isn't what I'm paying for.

I don't see any computer specs in your posts or your bio. By any chance do you have a Killer Networks ethernet card? Their software if not set correctly will limit your internet speeds.